Accurate monitoring of personal fluid consumption is vital for health. A variety of physiological and medical problems can arise with inappropriate fluid intake. For example, dehydration may increase the risk of cardiovascular strain, reduce heat tolerance, and reduce physical exercise performance. In addition, overhydrating may result in hyponatremia (low blood sodium levels) or other medical problems in some patient groups.
Quantifying the pattern and amount of fluid consumed over time by an individual is often fraught with inaccuracies. One approach is to ask individuals to only drink from a given personal container, to keep track of the fluid consumed from that container, and to carefully record the date, time, and amount of liquid consumed. The volume consumed is determined by reading the liquid level from graduations on a fluid container before and after drinking, and then calculating the difference. This approach is difficult under low-light conditions, and incorrect logbook entries are common. Inaccurate or inconsistent measurements often occur with prior art hydration devices, particularly at very low flow rates. At low flow rates, similar to rates produced by small sips, the amount of fluid consumed is often insufficient to fully engage a measurement sensor.
In U.S. Pat. No. 6,212,959, issued to Perkins, and incorporated herein by reference, a system for insuring proper human hydration is disclosed that includes an oral-suction-activated flow meter which measures and displays the volume of fluid withdrawn from a reservoir. Perkins suggests that a check valve, to prevent return flow of fluid from the user's mouth to the reservoir, is often adequate. In particular, Perkins' check valve is suggested as only allowing the flow of fluid in one direction. In use, the fluid flows from a bladder or fluid container, through the check valve and a fluid monitoring unit, and to the user through an outlet tube and mouthpiece. The check valve is meant to prevent the flow of fluid in the opposite direction, i.e., from the fluid monitoring unit back through the check valve. However, in practice, this arrangement appears to trap fluid in the top of the outlet tube (straw or mouthpiece) and requires a bite valve to prevent spillage. This bite valve may be problematic for elderly users or those with oral conditions that impair the user's ability to bite with sufficient force to actuate the bite valve.
In many prior art hydration devices, even if a one-way check valve is placed above the metering device and functions appropriately, there will still be a volume of liquid located within the flow measuring device, but below the check-valve, that will flow back toward its source and through the metering device actuating the metering device and generating erroneous fluid flow data. As a consequence, the check valve may allow fluid to flow in a reverse direction through the impeller thereby diminishing accuracy by allowing the impeller to rotate in an opposite direction.